Two-camera systems of the kind found in the newest smartphones have a pair of digital cameras facing the same direction. Each camera has a different lens: one camera has a lens with a short focal length, the other a lens with a long focal length. For instance, in some two-camera arrangements the short-focal-length lens can be a regular or wide-angle lens and the long-focal-length lens can be a telephoto lens with a 3× magnification compared to the wide-angle lens (i.e., if we designate the magnification of the regular or wide-angle lens to be 1×, the telephoto has triple the overall magnification, or 3X).
By themselves, these two-camera arrangements allow a user to capture only a wide-angle (1×) image or a telephoto (3×) image, and nothing in between. But what if the user wants to capture an image at an intermediate magnification that falls in between the two lens magnifications—say a 2× image in a system with 1× and 3× lenses? The focal lengths of the two lenses are fixed and cannot be changed, so true optical zoom cannot be implemented to create the 2× image. Nonetheless, to simulate optical zoom, images can be captured with both the 1× and 3× lenses and the captured digital images can be fused by known software methods to create an image that is substantially what would result if it was in fact possible to adjust the magnification of one of the lenses to 2×.
Problems arise with this simulated optical zoom if the difference in focal length between the short-focal-length lens and the long-focal-length lens becomes too large. In these situations, the algorithms that fuse images with different magnifications to form an image with a desired intermediate magnification have a difficult time creating a good image at the intermediate magnifications.